Digestion of coarse substances left on sewage screens in the sewage treatment



Sept. 1, 1931. v S K. IMHOFF 1,820,978

DI GESTION OF COARSE SUBSTANCES LEFT ON SEWAGE SCREENS :IN THE SEWAGE TREATIENT Filedflpv. '9, 192:;

mi M W for the purpose in question;

i Patented Sept. 1, 1931 UNI-Tan" sra'rasr-ATENT OFFICE more ois'nasina, GERMANY mqnszrron or come summons-LEFT, N snwaen scamms IN THE snwacn Application filed November fl mfllfsei-ial No.

The coarse substances left on s wage screens in'sewage treatment, cannot be disposed of in an odorless manner, because they decay in a very short time by a bad-smelling acid fermentation.- If thrown into a digestion chamber used for a digestion of sewage sludge, they remain generally as a' floating cover on the surface levelthereof and cannot be digested except with great difiiculty.

According. to the present invention, said drawback is overcome by bringing said coarse substances in contact with di esting sludge in alkaline fermentation an thor- 'oughly mixing it therewith, rior to their supply to the digestion cham er. By said thorough mixing the coarse substances are,

broken into small pieces, and their acid fermentation is obviated.

The accompanying drawings show by way of example how the inventlon can be put into practice:

Figs. 1 and 2 are respectively a vertical central section and a plan view of a. digestion chamber that is particularly adapted Beside a sludge digestion chamber a a rail track b is provided, along which the coarse substances are carried by tip cars,b ,;whence they are delivered into a mixin vessel 0. 3o Into the latter the digestingslu ge is supplied in a proportion of 2 parts of sludge to 1 part of coarse substances. A motor (2 with agitator e serves for mixing the sludge and coarse substances.

The digesting sludge is for example carri ed from the bottom 'of the sludge chamber through a ipe f; it can, however, also.be supplied rom another sludge chamber through a pipe branched off from the pipe .9,

' 40 this being'particularly required for starting the working of the sludge digestion chamber a.

.Upon the coarse substances being thoroughly mixed with the digesting sludge in the vessel 0, the latter is lifted by means ofan elevator indicated by the dotted lines a:

in Fig; 1. Then, the contents thereof are supplied from above through a hopper g'to' the digestion chamber a.

232,170, and in Germany September 3t), 1987.

heater a 'to which the digestion gases collected by the gas hood m with sieve-covered slots n at its circumference are supplied as fuel throu h a pipe h. From the heater a pipe in leads the hot water into the bottom end of the. digestion chamber. The excess water esca es through an overflow pipe (1 Z: the sur ace level of the digestion cham- In case that, in spite of the thorough mixing, a floating cover of undecomposed mat- The coarse substances require for their complete digestion a certain addition of water, which is attained by the supply of the hot water through the pipe 70. For. the same purpose,v however, -.digestion sludge from another digestion chamber can be supplied through the pipe 3 and a funnel .2 leading into the interior of the digestion chamber.

The alkaline fermentation, to which- I it is well to distinguish between the screenings or coarse substances taken from the sewage screens, and the sludge. 'ings consist of coarse substances which float on top and are removed by means of sieves, while the sludge isthe heavy matter that settles to the bottom and produces by its digestion the alkaline fermentation. Screenings, taken alone, are not productive,

actively at least, of the alkaline fermentation.

.In carrying out my invention, therefore, I take the screenings, which do not ferment on their own account in alkaline fermentation, and mix them with sludge which has already assumed the known state of alkaline The screen- The chamber is heated by means of a fermentation within the digestion chamber. I36

In the use of my method, under which the screenings are broken up and thoroughly intermixed with digesting sludge in alkaline fermentation and the resultant pseudosludge substance introduced into the diges- 'tion chamber, acid fermentation is obviated, and for further treatment it is unnecessary always to have at command a new or fresh supply of sludge, since through the pipe f m fPQllltllQ digestion chamber a, a supply of my hand.

sludge which is in a state of alkaline fer- 'mentation suitable for the mixing operation, can always be produced.

What I claim, is.

1. The combination of a digesting chamber to receive sludge, a movable vessel for receiving screening, a pipe in said chamber for conveying sludge to said vessel to mix with the contents therein, and a hopper through which the intermixed contents of said vessel can be discharged into the chamber.

2. The combination of a digesting chamber for sludge, a movable vessel to receive 5 screenings outside of said chamber, a pipe for conveying part of the sludge in the a chamber to said vessel to be mixed with the contents thereof and delivered to said chamher, and apipe mounted in said chamber in 3 position to convey undecomposed matter from the upper part of said chamber into said vessel on the outside thereof.

3. Steps 'in the method of digesting coarse sewage substances gathered from screens in the treatment of sewage, which steps consist in putting a batch of the coarse floatable screened-out sewage substances which do not of their own account ferment in alkaline fermentation, in a vessel sepa-.

rate from the vessel containing the sewage undergoing digestion, withdrawing from the sewage undergoing digestion the sludge settlings which are in a state of alkaline fermentation, intermixing the removed sludge scttlings with the coarse substances in the separate vessel, breaking up the coarse substances into fragments during the intermixing process to bring the'broken up fragments into direct contact with the alkaline sludge settlings so as to prevent odorous acid fermentation of the fragments and to produce a pseudo-sludge mixture, feeding the pseudo-sludge mixture into the sewage sludge undergoing digestion in a state of alka-line fermentation and continuing the digestion of the same together until the heavy inattcr settles as sludge settlings in alkaline fermentation, and thence repeating the aforesaid steps, withdrawing for each. ad-

'" mixture with each fresh batch of coarse substances a fresh supply of sludge settlings in alkaline fermentation.

In testimony whereof I have hereunto set KARL IMHOFF. 

